1. Field of the Invention
The present invention pertains to systems in which a working fluid is passed through a rotary machine including a rotor. More specifically, the invention pertains to power systems wherein a working fluid is heated and vaporized. The working fluid then being expanded to do work, as for example, in a turboexpander the rotor of which drives a shaft attached thereto.
In systems such as described above, the rotor and shaft are enclosed in a housing, and the housing and shaft typically have mating radial bearings and thrust bearings. Such bearings must be lubricated, and the usual way of doing this is by injecting a lubricant, under pressure, into the bearings through a lubricant passageway in the housing. The lubricant flows through each bearing, axially and circumferentially along the shaft. It is then drained from the bottom of the housing to a reservoir from which it is pumped back through the bearings again. Thus, a given quantity of lubricant is continually recycled through the system. Similarly, the working fluid is recycled. In a power system as described above, it is condensed after expansion and passed again through the heat exchanger.
There are several problems inherent in such systems particularly when the lubricant and the working fluid are chemically similar or are reactive with each other, when one is soluble in the other, or when they are otherwise incompatible in the sense that one interferes with the desired properties of the other. Two of the major problems in such cases are loss of working fluid and loss of lubricant viscosity and other properties, or conversely losses of lubricant and contamination of the working fluid thereby.
The turboexpander or other rotary machine must be sealed against atmosphere. This is generally accomplished by utilizing a seal around the shaft between the process zone, containing the working fluid and rotor, and the lubricant zone, containing the bearings and the remainder of the shaft. The seal should also serve to prevent the working fluid from leaking into the lubricant zone as this results in loss of working fluid and/or possible dissolution of the working fluid in the lubricant so as to reduce its viscosity or other necessary properties.
2. Description of the Prior Art
One previous method of sealing the process zone essentially utilized the bearing as a seal by pumping lubricant into the bearing with sufficient pressure that it would leak into the process zone and thereby seal the process zone against atmosphere while preventing leakage of working fluid into the lubricant zone. The major disadvantage of this system is that it requires a leakage of the lubricant, usually oil, into the process zone. Thus, the lubricant must be separated from the working fluid and collected so that they can be respectively recycled. Additionally, the heavy constituents of the working fluid become dissolved in the lubricant, interfering with its lubricating properties and also depleting the amount of and changing the composition of the working fluid. This is most undesirable since only the slightest amount of working fluid loss is tolerable in such systems.
Other types of seals have been used. Many of them must be lubricated by oil which leaks into the process zone introducing problems similar to those described above. In any event, there has generally been danger of leakage in one direction or the other in prior art systems regardless of what type of sealing system was used.